The lithium battery has recently been widely used for example, as an electric source for driving small-sized electronics. The lithium battery has a basic structure comprising a positive electrode, a negative electrode, a separator and a non-aqueous electrolytic solution, which are contained in a cylindrical, square-shaped or coin-shaped cell. The positive electrode generally comprises a complex oxide of lithium such as LiCoO2. The negative electrode generally comprises carbonaceous material or metallic lithium. The separator for the lithium battery comprises a porous film formed of polyolefin such as polyethylene (PE) and polypropylene (PP) or a laminated porous film comprising one porous polyethylene film interposed between two porous polypropylene films.
In a process for preparation of a cylindrical lithium secondary battery, the battery has been prepared for example, by laminating positive and negative electrode sheets and a separator, winding the laminate around a metallic winding pin to form a battery element (in the form of a spirally wound roll), placing the roll in a battery cell, and injecting a non-aqueous electrolytic solution into the cell. The recent lithium secondary battery has a higher capacity as a result of development competition. In a general way of enlarging the capacity, volume of electrode active materials increases in a battery cell with a limited size, while volume of the other substances decreases. Accordingly, density of electrode composite including the electrode active materials becomes increased, and thickness of the electrode composite becomes increased. In contrast, a current collector of the electrode composite and the separator are required to have a small thickness. Since the remaining space in the cell becomes extremely small, it is difficult to inject the non-aqueous electrolytic solution into the cell. It becomes difficult and takes a long time to inject the electrolytic solution into the cell. It is also difficult to impregnate the separator uniformly with the non-aqueous electrolytic solution.
Japanese Patent Provisional Publication No. 6-333550 discloses an invention of making a rough surface on a separator to make it easy to inject a non-aqueous electrolytic solution into a cell in which a roll of the separator and electrode sheets is placed. The publication further describes that plural grooves are provided in a width direction of the separator in addition to the rough surface.